1. Field of the Invention
The present invention relates to an optical apparatus composed of a light source and an optical component, for example, an optical apparatus such as a light output monitor of a light source provided in an optical pickup installed in an optical recording and reproducing apparatus, and a method for adjusting the amount of light of the same.
2. Description of the Related Art
Some information recording and reproducing apparatuses using an optical recording method record on and reproduce from plural kinds of optical recording mediums based on various standards, such as a compact disk (abbreviated as CD) and a digital versatile disk (abbreviated as DVD). FIG. 10 is a view showing a structure of a major part of a conventional optical pickup apparatus 1. FIG. 10 shows the optical pickup apparatus 1 structured so as to have two light sources, that is, first and second light sources 2, 3 in order to record on and reproduce from two kinds of recording mediums (hereafter, sometimes referred to as optical disks) having different standards by using a single optical pickup.
In the optical pickup apparatus 1, a first light beam 4 emitted from the first light source 2 is mostly reflected by a beam splitter 5 and enters a collimator lens 6, is made to become a parallel ray by the collimator lens 6 and enters an objective lens 7, and is converged by the objective lens 7 and applied to an optical disk 8 as a light spot having a minute diameter. Moreover, a second light beam 9 emitted from the second light source 3 is mostly transmitted by the beam splitter 5 and enters the collimator lens 6, is made to become a parallel ray by the collimator lens 6 and enters the objective lens 7, and is converged by the objective lens 7 and applied to the optical disk 8 as a light spot having a minute diameter.
The optical pickup 1 is generally provided with a monitor light receiving element 10 so as to monitor the amount of light of the first light beam 4 emitted from the first light source 2 or the second light beam 9 emitted from the second light source 3, and APC (automatic power control) is executed so that the amount of emission light of the first light beam 4 emitted from the first light source 2 or the second light beam 9 emitted from the second light source 3 is controlled to a proper value on the basis of a signal detected by the monitor light receiving element 10.
FIG. 11 is a view showing a state where a light output of the first light source 2 is monitored, and FIG. 12 is a view showing a state where a light output of the second light source 3 is monitored. In light output monitor regarding the first light source 2, part of the first light beam 4 emitted from the first light source 2 is transmitted by the beam splitter 5 to become a first transmission light beam 11, and the first transmission light beam 11 is made enter the light receiving element 10. Moreover, in light output monitor regarding the second light source 3, part of the second light beam 9 emitted from the second light source 3 is reflected by the beam splitter 5 to become a second reflection light beam 12, and the second reflection light beam 12 is made enter the light receiving element 10.
However, in the related art, the amount of light made enter the collimator lens 6, that is, light used for recording and reproducing information is preferentially made larger, so that only approximately 1% to 5% at most of light emitted from the light source is guided to the monitor light receiving element 10.
Particularly, in recent years, increase of the amount of light reaching the surface of an optical disk as much as possible is required as an optical disk apparatus becomes capable of high-speed recording and reproducing, so that the actual situation is that it is impossible to decrease the amount of light used for recording and reproducing information in order to increase the amount of light for monitor. There is such a relation between the amount of light for monitor and the amount of light used for recording and reproducing information that one has to be decreased when the other is increased, and it is difficult to increase both of them at the same time.
Further, light applied to the light receiving element 10 is divergent light, and the area of the light applied to the light receiving element 10 is far larger than a light receiving portion 13 serving as a light detecting portion disposed to the light receiving element 10. In contrast, the light receiving portion 13 has been further miniaturized so as to increase the sensitivity thereof in recent years. Therefore, there is a problem such that the amount of light detected by the light receiving portion 13 is small, that is, the level of a detection signal is small.
Still further, the size of the light receiving portion 13 is approximately 0.7 mm in diameter in the present circumstances, whereas there are variations as large as approximately ±0.3 mm in the accuracy of installation of the light receiving portion 13 to the external dimension of the light receiving element 10. Therefore that there is a problem such that the level of a signal detected by the light receiving element 10 largely varies according to each optical pickup apparatus. Furthermore, in a case where an installation position of the light receiving portion 13 in the light receiving element 10 is not in and around the center of the light receiving element 10 but leans to a peripheral portion thereof, the light receiving portion 13 is disposed so as to lean to a side of the top surface or the bottom surface of the light pickup apparatus. When the position of the light receiving portion 13 leans in this manner, a periphery portion of the light spot with a weak strength is detected, so that the level of a detection signal becomes small, and there is a problem such that stable control of a light output is difficult.
In one of related arts to solve these problems, a best-suited condensing lens to an optical system of an optical apparatus in order to condense light to a light receiving portion is used and fixed in a predetermined position. Moreover, in another related art, a light receiving element unit such that a light receiving element is embedded in a block with a light entering surface formed on a focusing surface so as to face the entering surface is used (refer to Japanese Unexamined Patent Publication JP-A 5-264338 (1993)).
However, these related arts have problems as described below. It is necessary to produce a condensing lens or a light receiving element unit with a lens surface dedicated for each optical apparatus. Moreover, since it is difficult to respond to variations of individual light receiving elements, there arises loss in the amount of light. Further, it is necessary in correction of the optical apparatus or the light receiving element, to process so as to newly form an attachment portion to a fixture surface, or to remake the light receiving element unit, which is a great disadvantage in the respect of the cost of manufacturing.